In general, secondary batteries are chargeable and dischargeable, unlike primary batteries that are not chargeable. Recently, high-output secondary batteries using a non-aqueous electrolyte having high-energy density are being developed. In a case of a low-capacity battery in which one battery cell is packaged in a pack shape, the low-capacity battery may be used in portable small electronic devices such as mobile phones, notebook computers, camcorders, and the like. It large-capacity power, such as power for driving motors of electric vehicles, is needed, a plurality of battery cells are connected in series or parallel to each other to constitute a large-capacity secondary battery package.
FIG. 1 is an exploded perspective view of a secondary battery. As illustrated in FIG. 1, a secondary battery includes an electrode assembly 2, a can 1 for accommodating the electrode assembly 2 therein, and a top cap for sealing an upper portion of the can 1. A separate having a sheet shape is disposed between a cathode having a sheet shape and an anode having a sheet shape. In this state, the cathode, the separator, and the anode are wound, and anode and cathode terminals are provided to protrude, thereby manufacturing the electrode assembly 2. The can 1 for accommodating the electrode assembly 2 may be provided as a plate that is formed of an aluminum alloy.
The top cap may be assembled with an upper portion of the can 1 to seal the upper portion of the can 1 that is opened to accommodate the electrode assembly 2. The top cap includes a top plate 110 and an insulator 7 disposed between the can 1 and the top plate 110 and formed of a plastic material.
FIG. 2 is a schematic view of the top plate 110. As illustrated in FIG. 2, a filling hole 120 through which an electrolyte is filled is defined in one side of the top plate 110 to pass through the top plate 110. The electrolyte is injected into the can 1 through the filling hole 120.
After the electrolyte is injected through the filling hole 120, the filling hole 120 is sealed. FIGS. 3 and 4 are schematic views illustrating a process of sealing the filling hole according to the related art. As illustrated in FIGS. 3 and 4, a separate metal ball 130 is provided. In the related art, to sealing the filling hole 120, the separate metal ball 130 is used. That is a physical force may be applied to the metal ball 130 to press-fit the metal ball 130 into the filling hole 120. As described above, the metal ball 130 may be only press-fitted through the physical force to primarily seal the filling hole 120, or additional laser welding may be performed after the metal ball 130 is press-fitted to secondarily seal the filling hole 120. Thereafter, epoxy may be additionally applied to an upper portion of the portion at which the metal ball 130 is press-fitted to finally seal the filling hole 120.
However, in the method of sealing the filling hole according to the related art, since the separate metal ball 130 is needed, manufacturing costs may increase, and manufacturing process may be complicated.